This invention relates to geothermal wells and in particular, to a new and improved method and apparatus for interconnection of a geothermal well and a thermal energy use plant.
A geothermal well installation typically comprises a well with a well head which provides a two-phase mixture of steam and water (usually brine), a thermal energy use plant such as a chemical process plant or an electric generating plant, and a transmission pipeline linking the well head to the energy use plant. The two-phase mixture often flows in the well and/or the pipeline in slug or other nonuniform flow. This nonhomogeneous or non-steady or pulsing type flow creates problems in the plant and in the pipeline itself. Conventional installations typically have a first stage separator located near the well head, and separately transmit the separated steam and water phases from the separator to the plant. The pressure and flow fluctuations resulting from the instabilities mentioned above are transmitted through the steam and water transmission lines. It is generally recognized that some economy may be achieved by using a single two-phase pipeline to transmit the geothermal fluid from the well head to the plant where the first stage separator is located. In this case the flow instabilities are increased because of pipeline restrictions described in the next paragraph.
It has been found that flow instability of the two-phase fluid in the pipeline between a geothermal well head and an energy use plant is caused and/or increased by restrictions in the line between the well head and the plant or first stage separator. This instability causes what might otherwise be a time-wise steady or uniform two-phase flow condition in the well and pipeline system to become and remain nonsteady or nonuniform. The restrictions may take various forms, such as a control valve or other restricting orifice, a vertical rise or a vertical expansion loop, a change in slope which causes accumulation of liquid, an elbow of relatively short radius which promotes separation of liquid droplets from the gas, and the like.
It is an object of the present invention to provide a new and improved method and apparatus for transmitting two-phase fluid from a geothermal well head to an energy use plant and maintaining homogeneous two-phase flow with a minimum of instabilities. A further object is to provide such a method and apparatus utilizing a pipeline directly connected to the well head and having substantially no flow restrictions in the line.
It has been found that any flow instabilities in the unrestricted pipeline can be further removed by inserting a decoupling tank between the pipeline and the energy use plant, with the decoupling tank providing flow of water and steam to the plant in a substantially steady mode suitable for use at the plant.
Accordingly, it is a further object of the invention to provide such a method and apparatus incorporating a decoupling tank. An additional object of the invention is to provide specific configurations for a decoupling tank. In one configuration the decoupling tank should be as close as practical to the plant whereas in another configuration with single phase output lines it can be as close to the well as practical. However for economy of piping, it may be advantageous to locate the decoupling tank for this latter case also close to the plant.
In the past, it has typically been the practice to position a separator at the well head or at some distance from the well head to separate steam and water, and transmit the steam via a pipeline to the plant, with the water also being transmitted to the plant or returned to the reservoir by a reinjection well or otherwise, as desired. Typically, some form of throttling or flow-control valve is positioned at the well head or in the transmission line to the separator, which usually incorporates elbows, tees, slope changes, vertical risers, vertical expansion loops, and the like, all of which produce instability of flow in the form of water slugs in the steam.
One proposed system in U.S. Pat. No. 3,605,403 shows a pipeline directly connecting the well head to a power station, without describing the pipeline and without incorporating any decoupling tank or other provision for achieving a steady uniform flow in the pipeline.
It is an additional object of the present invention to provide a new method and apparatus for two-phase fluid transmission which is an improvement over that known in the prior art.
Other objects, advantages, features and results will more fully appear in the course of the following description. The drawings merely show and the description merely describes preferred embodiments of the present invention which are given by way of illustration or example.